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1.~nonNUInericalmodellingbythefiniteelement(FE)methodhasbecomeaneffectiveandeconomyicmeansforsimulatingmetalfoeingprocesses.However,accuratemodellingdemandsthecorrectdefinitionandinputsofthedataforthethermalandphysicalpIDPertiesoftheworkpieceandtoolmaterials,theboUndaryconditionsattheworkpiece--toolinterfaceandinotherareas,inadditiontoappropriatemeshgenerationandnumericalsolutions.Althoughmostofthematerialdataareavailable,thedataforinterfacialheattransferandfrictionconditions,Whichhavesubst… 相似文献
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Sellars A.G. MacGregor S.J. Farish O. 《Dielectrics and Electrical Insulation, IEEE Transactions on》1995,2(1):46-53
The paper describes a technique for simulating the presence of partial discharges in gas-insulated substation (GIS) equipment. The technique employs a pulse generator to inject current pulses through a suitable protrusion. The current pulses have similar temporal characteristics to those produced by an actual discharge event, with the added advantage that their magnitudes can be controlled accurately. Because the pulses are highly reproducible, they are ideally suited for investigating the UHF technique of partial discharge detection. The paper discusses the relationship between the magnitude of the UHF signal received by a coupler and the discharge magnitude. It also shows that the coupler signal is dependent on the protrusion length and on the spatial relationship between the protrusion and the coupler. The implications for practical discharge measurements in GIS also are discussed 相似文献
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Sellars M.P. Greaves S.D. Porter J. Crosby D.B. Freeman B.R. 《Electronics letters》2003,39(7):624-625
A precoding technique for pre-equalising contention bursts in a slotted-ALOHA access request scheme, for use in single-carrier broadband fixed wireless access (FWA) networks is presented. Multipath channel distortion is compensated for at the transmitter, so that the contention burst arrives undistorted at the receiver. 相似文献
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Steels containing 0.2 pet C and 0 to 12 pct Cr have been tempered for different times or recrystallized at 700°C and subsequently
tensile tested at 100°C temperature intervals in the range 0° to 700°C. At all temperatures, the strength of the as-tempered
steels depends primarily on the dislocation structure inherited from the martensite transformation and work softening observed
during deformation at 600° and 700° is attributable to recovery of this structure. Strain enhanced precipitation of M3C is observed after deformation at 200° to 600°C in all the steels, independent of the nature of the carbide present after
tempering. Serrated yielding occurs at temperatures increasing from 200° to 400°C with increasing chromium content and is
associated with an increase in strength and strain-hardening rate in all cases. It is concluded that dynamic strain-aging
results from dislocation locking by chromium-interstitial complexes in the alloy steels.
T. Mukherjee, formerly Research Student, Department of Metallurgy, University of Sheffield, Sheffield England.
This paper is based upon a thesis submitted by T. Mukherjee in partial fulfillment of the requirements of the degree of Doctor
of Philosophy at the University of Sheffield. 相似文献
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A transnasal trans-sphenoidal surgical approach to the pituitary gland is described. The operative and post-operative experiences with the use of this technique on 21 patients with hormone-dependent malignant disease are reported. In 2 patients the procedure was abandoned because of intrasellar haemorrhage and in 1 an empty sella was found. Fifteen patients developed diabetes insipidus and 1 patient died in the postoperative period. 相似文献
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Two experiments were conducted to determine the effect of estradiol cypionate (ECP), when incorporated into a conventional GnRH-PGF2α-GnRH timed artificial insemination protocol (Ovsynch), on systemic estradiol (E2), time and incidence of ovulation, luteal development, and conception rate in Holstein cows. Our objective was to determine if administration of 0.25 mg of ECP at the time of the second GnRH injection would effectively synchronize ovulation and increase conception rate. In Experiment 1, lactating Holstein cows (n = 23; 58.7 ± 1.2 d in milk) were synchronized with PGF2α (at d −10). Ten days later, Ovsynch was initiated with the administration of 100 μg of GnRH (d 0) followed by PGF2α on d 7. On d 9, cows were assigned randomly to be treated with either GnRH + 0.25 mg of ECP (OVS-ECP; n = 11) or GnRH and 1 mL of cottonseed oil (OVS-C; n = 12). Ovarian activity was monitored by ultrasonography on d 0, 7, and 9. To determine the time of ovulation, ultrasound examinations were conducted at 12 and 20 h posttreatment and then at least every 3 h until either 36 h posttreatment or ovulation was observed. Blood samples were collected on d 0, 7, 9, and 16 for progesterone analysis. Blood samples also were collected at the time of treatment (d 9, 0 h) and at 6, 12, 20, and 28 h for E2 analysis. Incidence of ovulation did not differ between treatments. Mean ovulation time relative to the second GnRH administration was similar between treatments. Serum progesterone concentration did not differ between treatments at any time. Serum E2 concentration was not different at the time of treatment (0 h); however, mean E2 concentration was greater for the OVS-ECP group at 6 and 12 h after treatment compared with OVS-C. In Experiment 2, lactating dairy cows (n = 333) in 3 commercial herds were randomly assigned to OVS-ECP (n = 169) or OVS-C (n = 164). Cows were inseminated 22 to 24 h posttreatment. Conception rates did not differ between treatments. Estradiol cypionate treatment was successful in increasing serum E2 when administered at the time of the second dose of GnRH in the Ovsynch protocol. Conception rates, however, were not affected by treatment. 相似文献
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M. Krzyzanowski J. H. Beynon C. M. Sellars 《Metallurgical and Materials Transactions B》2000,31(6):1483-1490
Both numerical analysis based on finite-element (FE) modeling and experimental evidence concerning the secondary oxide-scale
failure at entry into the roll gap are presented and reviewed for a better understanding of events at the roll-workpiece interface,
in turn, leading to better definition of the boundary conditions for process models. Attention is paid to the two limit modes
leading to oxide-scale failure, which were observed earlier during tensile testing under rolling conditions. These are considered
in relation to the temperature, the oxide-scale thickness, and other hot-rolling parameters. The mathematical model used for
the analysis is composed of macro and micro parts, which allow for simulation of metal/scale flow, heat transfer, cracking
of the oxide scale, as well as sliding along the oxide/metal interface and spallation of the scale from the metal surface.
The different modes of oxide-scale failure were predicted, taking into account stress-directed diffusion, fracture and adhesion
of the oxide scale, strain, strain rate, and temperature. Stalled hot-rolling tests under controlled conditions have been
used to verify the types of oxide-scale failure and have shown good predictive capabilities of the model. The stock temperature
and the oxide-scale thickness are important parameters, which, depending on other rolling conditions, may cause either through-thickness
cracking of the scale at the entry or lead to entry of a nonfractured scale when the scale/metal interface is not strong enough
to transmit the metal deformation. 相似文献
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Microstructural development during warm rolling of an IF steel 总被引:3,自引:0,他引:3
Wedge-shaped slab rolling was employed to investigate the microstructural evolution of an interstitial-free (IF) steel during warm working in the temperature range 500–800°C. Mean flow stress-strain curves calculated from load-time data of rolling tests reasonably correspond to work hardening and dynamic recovery behaviour. The development of substructures in the deformed material was investigated using optical and electron microscopy. A close correlation was observed between mechanical behaviour and microstructural development during deformation. Microbands in directions of ± 35° with respect to the rolling direction, independent of strain, temperature and initial grain orientations are the most noticeable features in the microstructural observations. The sequences of substructural changes from the appearance of early microbands at very low strains, their development with strain, to the formation of equiaxed subgrains at higher strains and temperatures were followed by TEM. 相似文献